Some switch-mode power converters include transformers that provide a galvanic isolation layer between the power source and the load. A controller may regulate the voltage output by the power converter. The controller may receive a feedback voltage proportional to the output voltage to more accurately regulate the output voltage. Some controllers receive a feedback voltage from the secondary-side of the transformer, such that the feedback voltage must cross the isolation layer, which may require complicated and/or costly circuitry for the feedback voltage to cross the isolation layer. Some controllers control the power converter based on a feedback voltage generated by an auxiliary winding on the primary-side of the transformer. For example, a controller may detect a “knee point” in the feedback voltage and cause the power converter to adjust the output power in response to detecting the knee point. However, controllers that utilize the feedback voltage from the auxiliary winding may still be relatively complex and costly, and may not accurately detect the knee point voltage.